AU2008240366A1 - Mobile object position determination - Google Patents
Mobile object position determination Download PDFInfo
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- AU2008240366A1 AU2008240366A1 AU2008240366A AU2008240366A AU2008240366A1 AU 2008240366 A1 AU2008240366 A1 AU 2008240366A1 AU 2008240366 A AU2008240366 A AU 2008240366A AU 2008240366 A AU2008240366 A AU 2008240366A AU 2008240366 A1 AU2008240366 A1 AU 2008240366A1
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- 238000002604 ultrasonography Methods 0.000 claims description 50
- 230000005540 biological transmission Effects 0.000 claims description 36
- 230000004044 response Effects 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 3
- 230000008569 process Effects 0.000 claims description 2
- 238000012360 testing method Methods 0.000 description 8
- 238000001514 detection method Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 230000033001 locomotion Effects 0.000 description 4
- 238000013459 approach Methods 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012417 linear regression Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/74—Systems using reradiation of acoustic waves, e.g. IFF, i.e. identification of friend or foe
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
- G01S5/30—Determining absolute distances from a plurality of spaced points of known location
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- General Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Computer Networks & Wireless Communication (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Description
WO 2008/129295 PCT/GB2008/001412 Mobile Object Position Determination 5 This invention relates to communication between a static base and a mobile object and/or to the determination of the presence and/or position of a mobile object. It relates particularly, although not necessarily exclusively, to the use of ultrasound. When viewed from one aspect the invention provides an ultrasound position 10 determination system comprising a base unit and at least one mobile unit, each of said mobile and base units operable to transmit and receive ultrasonic signals, said mobile unit being adapted to transmit a predetermined signal in dependence upon the state of transmission of the base unit, said base unit being adapted to determine the time taken for said signal to pass from the mobile unit to the base unit and thereby calculate a 15 distance between the mobile unit and the base unit. When viewed from a second aspect the invention provides an ultrasound position determination system comprising a base unit and at least one mobile unit, said mobile unit being adapted to transmit an ultrasonic signal in response to a signal from the 20 base unit, said base unit being adapted to determine the time taken for said ultrasonic signal to pass from the mobile unit to the base unit and thereby calculate a distance between the mobile unit and the base unit. The Applicant has identified a desirability for a system in which a base unit is able to 25 determine information about the position of one or more mobile units, particularly over a short range such as within a room in a building. There are many possible applications of this. One potential, non-limiting, example application envisaged by the Applicant is a system for determining the presence of any of a number of tags in a room in a house in which a television set is situated in order to be able automatically 30 to log television audience data. Preferably the system comprises a plurality of mobile units moveable independently of each other. Preferably each mobile unit has only one ultrasound transmitter.
WO 2008/129295 PCT/GB2008/001412 2 In preferred embodiments of the invention the time taken for said ultrasonic signal to pass from the mobile unit is calculated from the aggregate time for the signal to be transmitted from the base unit to the mobile unit, and for the response to be received 5 from the mobile unit. If the delay between reception of the signal at the base unit and transmission of its reply is known, the total time will be the sum of the propagation times of the signal and reply. Where the signals are of the same type, i.e. both ultrasound signals, the propagation times might be assumed to be the same and hence an average can be calculated. In another alternative the request signal from the base 10 unit to the mobile unit might be significantly faster than the reply, e.g. by using a signal from the electromagnetic spectrum, and therefore its propagation time might be negligible. However there are also other possibilities. For example it might be possible to take into account movement between the mobile unit and the base unit between reception of the request and transmission of the response. 15 In some embodiments of the invention the mobile unit is configured to detect a break in transmission by the base unit and to transmit thereafter. This can be implemented in a manner similar to that for avoiding collisions between transmitters whereby a transmitter will not transmit if it detects that another transmitter is already 20 transmitting. However to be able to measure the distance between the base unit and the mobile unit in accordance with the invention, the time at which the mobile unit transmits its signal needs to be known - e.g. by making it a predetermined time after a cease of transmission by the base. 25 As mentioned above, a system in accordance with the invention could work with just one mobile unit or with a plurality. When a system has a plurality of mobile units each could be assigned a unique delay from the cessation of transmission by the base unit before transmitting its signal to the base unit. This is one way of ensuring that the mobile units do not transmit at the same time and avoids the need for each mobile 30 unit to transmit identifying information. However this is not essential.
WO 2008/129295 PCT/GB2008/001412 3 In some embodiments the mobile unit is configured to detect a specific signal from the base unit - e.g.. a particular frequency, change of frequency or sequence of transmissions. A single mobile unit or a plurality thereof could be used. Multiple mobile units could be configured to respond to the same specific signal from the base 5 unit or could be configured to respond to different signals. If they respond to the same signal they are preferably configured to do so in different timeslots, but this is not essential. For example they could instead respond in a non-predetermined sequence but include identification information; or one or more of the responses could include a spread spectrum signal such that collision avoidance is not necessarily 10 required. Preferably the mobile units in a system comprising multiple mobile units are able to distinguish between transmissions from the base and transmissions from other mobile units. One or any combination of for example duration of transmission, pattern of 15 transmission, frequency, or codes could be used to provide such distinction. The determination of position in accordance with the invention is not intended to imply any limitation as to accuracy. For example the determination could be of coordinates in one, two or three dimensions, or could simply determine whether the 20 mobile unit is in one or more zones. At the simplest level the determination of position could simply determine whether the mobile unit was within a predetermined distance of the base unit or not. When viewed from a third aspect the invention provides an ultrasound position 25 determination system comprising a base unit and at least one mobile unit, said mobile unit being adapted to transmit an ultrasonic signal in response to a signal from the base unit, said base unit being adapted to determine the time taken for said ultrasonic signal to pass from the mobile unit to the base unit and thereby determine whether the mobile unit is within a predetermined distance from the base unit. 30 WO 2008/129295 PCT/GB2008/001412 4 As with the earlier aspects of the invention it is preferred that the system comprises a plurality of mobile units moveable independently of each other. Preferably each mobile unit has only one ultrasound transmitter. 5 When viewed from a fourth aspect the invention provides a base unit configured to transmit a signal to a mobile unit comprising a transmitter configured to transmit a signal to one or more mobile units, and an ultrasound receiver configured to receive an ultrasonic signal from the or one of the mobile units, said base unit being adapted to determine the time taken for said ultrasonic signal to pass from said mobile unit to 10 the base unit. Preferably the base unit is configured to receive and process only ultrasonic signals from only one mobile unit at a time. 15 When viewed from a fifth aspect the invention provides a mobile unit comprising a receiver configured to receive a request signal from a base unit and an ultrasonic transmitter configured to transmit an ultrasonic signal to said base unit after a predetermined time from receipt of said request signal. 20 The ultrasonic signal from the mobile unit could be used just to determine the distance of the mobile unit from the base unit. However this is not essential. For example the signal could include other information such as identification or status information. The status information could include movement status or history; or battery status. Indeed any other information could be included in the signal. Equally such other 25 information could additionally or alternatively be transmitted at other times. The mobile unit is also referred to herein as a 'tag'. Such a tag is conveniently and preferably in the form of a self-contained device containing the ultrasound transmitter and receiver and associated processing. Preferably the tag comprises its own power 30 supply - e.g. a battery. However none of these features is essential. For example a tag could be an integral part of a larger object or device. It is to be understood therefore that 'tag' and 'mobile unit' are interchangeable.
WO 2008/129295 PCT/GB2008/001412 5 Ultrasound is normally understood to mean longitudinal pressure waves in any medium, e.g. air, having a frequency above the normal human hearing range. This is typically taken as being above 20 kHz, although in preferred embodiments of the 5 invention a frequencies between 30 and 50 kHz are used. Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 10 Fig. I is simplified schematic diagram of an object position detection system embodying with the invention; Fig. 2 is schematic diagram of the components of a mobile unit for use with the embodiments of the invention; 15 Fig. 3 is a simple flow diagram describing part of the operation of the mobile unit; Fig. 4 is a timing diagram illustrating the operation of a system embodying the invention; 20 Figs. 5 to 8 are timing diagrams for various alternative embodiments; Fig. 9 is a plot of base tag current vs. sound pressure from a responding tag in a test system; and 25 Fig. 10 is graph of distance between transmitter and receiver vs. time difference between transmission and receipt achieved in an experiment to determine the tag's time delay. 30 Fig. I shows a simplified schematic diagram of an embodiment of the invention. This embodiment allows the separation of a mobile tag 2 from a base station 4 to be determined. Although only one tag is shown for simplicity a system in accordance WO 2008/129295 PCT/GB2008/001412 6 with the invention will typically include a number of tags which are moveable completely independently of each other. First the base unit transmitter 6 transmits a predetermined ultrasound pattern. As will 5 be described later, there are many possible patterns could be employed but for this simple system with only one tag a simple break in a continuous transmission can be used for example. When the tag's receiver 8 receive the signal (or instead stops receiving it) the control 10 electronics in the tag 2 will generate a reply signal via the tag's transmitter 10. This reply signal is then received by the receiver 12 of the base unit. The base unit 4 is thus able to measure the time taken for the signal it transmitted to be received and processed by the tag 2 and for the reply to be received. 15 The base unit can then determine the distance d as follows: The speed of sound v in air is given by the following equation: v z (331.4+0.6T)m / s Equation 1 20 Where Tc is the temperature in Celsius. The speed v can also be expressed by the following equation: v= 1 Equation 2 ti - to Where 1 is the distance (range) in meters travelled by a signal between the two points 25 in time to and t 1 . The distance 1 can be derived using Equation I and Equation 2: S= (t 1 - to)v = (t - to)(331,4 + 0,6T) Equation 3 The separation of the ultrasound tag 2 and the base station 4 can now be found by 30 measuring the time of flight (TOF) between the base and the arrival of a tag's response at the detector, i.e. by measuring the time ti in Equation 3 above. In the WO 2008/129295 PCT/GB2008/001412 7 simplest case it can be assumed that the distance d between them is twice the distance measured since the signal must travel to the tag 2 and the response travel back to the base 4. Compensation must be made for the processing delay at the tag 2 between detection of the signal and transmission of the response, e.g. by measuring the TOF 5 when the tag is at a known distance from the base. This simplistic illustration demonstrates the principle on which other embodiments of the invention are based. On each of the tag 2 and the base 4 the transmitter and receiver are shown as separate form one another merely for the purposes of 10 illustration - they could indeed be separate but equally they could employ the same transducer. An exemplary receiver circuit for the tag 2 will now be outlined with reference to Figure 2. The circuit comprises an ultrasound transducer 14 which can be operated in 15 both transmit and receive modes. A switch 16 is used to switch the transducer between these two modes. The switch 16 is controlled by a micro-controller 18. When in transmit mode the micro-controller 18 sends a signal to a driver 20 for the transducer to cause it to drive the transducer 14 to produce a signal.. When the switch is in receive mode, the output from the transducer is fed to an amplifier 22 which then 20 feeds the signal to a comparator 24 to convert it into a binary 1 or 0. This is then fed back to the microcontroller 18. In a simple embodiment, the tag is arranged to transmit a response signal when it detects a gap in transmission from the base; i.e. it waits for the channel to become 25 free. This is similar to functionality proposed for ultrasound tags to prevent conflicting transmissions between multiple tags, but is here employed for a different purpose. In such use the tag will generally stand-by in receive mode monitoring transmissions 30 it receives. As long as the transducer 14 picks up a signal on the appropriate frequency, e.g. from the base, the tag remains in receive mode. However as if a break in transmission is detected, the micro-controller 18 sends a signal to the switch 16 to WO 2008/129295 PCT/GB2008/001412 8 switch to transmit mode and another to the driver 20 to generate a reply signal to be transmitted by he transducer 14. The micro-controller may be programmed to initiate the response signal as soon as a break in transmission is detected (albeit with a small inherent delay being inevitable) or after a predetermined deliberate delay. 5 Another possibility would be to await a specific signal from the base. An exemplary flowchart of such a routine is shown in Fig. 3 and is described below. The tag starts its main loop by measuring its battery level at 24 so that this can be 10 reported to the base station in the tag's message. Thereafter, a second loop is entered whereby the tag starts listening for ultrasound at 26. If ultrasound is detected then a comparison is carried out at 28 to determine whether it is within a predefined frequency interval. If so then at 30 the number of frequency leaps is counted. 15 When the tag detects a break in transmission (i.e. the ultrasound is no longer detected, it determines at 32 whether a sufficient number of frequency leaps has been detected to indicate a base request signal. If a sufficient number have been detected a response will be sent at 34. This message, or the timing of its transmission, will identify the tag and also contain information regarding the battery status determined at step 24. 20 If an insufficient number of frequency leaps to indicate a base request have been detected then the tag returns to step 26 to standby listening for ultrasound. Even if a base request message is not detected, if a threshold time has passed since the 25 last message was sent (box 36), a message 34 will be sent anyway. The ultrasound message in either type of system could contain information about battery status, whether a valid request has been detected (i.e. whether it is a 'timeout' message or not), and also whether the tag is in motion or not. 30 In accordance with the first mode of operation set out above, the base transmits ultrasound signals uninterrupted for a predetermined period, forcing tags to wait in WO 2008/129295 PCT/GB2008/001412 9 standby without transmitting. The base then stops transmitting for a moment to enable the tag(s) to transmit an ultrasound message which is received by the base. The base can then start transmitting again after the message is received from the tag(s). 5 A simple illustration of this scheme with one tag is shown in Figure 4. The base transmits ultrasound noise (uninterrupted repeated messages) until time to. At this time, the 'line' becomes free and once this is sensed by the tag it will start to transmit an ultrasound message response at time ti. The message is received at the base at time t 2 . The base then recommences transmission, after a short delay, at time twait . The 10 described arrangement therefore allows simple periodic polling of a mobile ultrasound transmitter tag. This allows the base to calculate the time of flight from the difference t2 - tI taking into account the tag's (previously determined) transmission delay. From this the distance of the tag from the base can be calculated. This can be used in many varied applications. For example it could be used as a simple proximity detector to 15 initiate an action such as switching on a light or opening a door when a tag is within a predetermined range. An exemplary extension of the scheme described above with reference to Fig. 4 can be adapted to accommodate multiple tags by programming each tag to wait a different 20 preset period tx before it responds. This is shown in Fig. 5. Thus after the base halts transmission at time to, the first tag transmits a message at time ti. The second tag transmits its message at time tI+t 2 . As can be seen the delay in transmission t 2 between the first and second tags is greater than the time for the first tag transmits in order to avoid collision. Figure 5 shows the base resuming transmission after each tag 25 has responded once but this is not essential. For example the sequence could be repeated any number of times or even continuously after each base transmission break. The base might be able to resume transmitting during the sequence to interrupt it and start again. 30 An alternative approach to simply waiting for a gap in transmission is for the tag to identify a specific base request message, e.g. using the tag receiver routine described above with reference to Fig. 3. The base request message can, for example, be a long WO 2008/129295 PCT/GB2008/001412 10 message (e.g. multiple messages sent non-stop). By incorporating a counter that increments each time a valid frequency is sensed, (see step 30 in Fig. 3), the tag can then be capable of distinguishing a base request from a standard ultrasound message which would correspond to a lower count than the base request. 5 Alternatively a tag may be able to calculate an estimate of the frequency of an ultrasound signal it receives. In other words, a request can be generating by sending a message using only one (or more) frequencies. The tag will only respond to a message with a given frequency (within a given frequency range). An example using a single 10 tag is shown in Figure 6. Figure 7 shows one way of accommodating multiple tags. Each tag is programmed to wait a given period t, before it responds to a base request, as shown. This is therefore similar to the scheme described with reference to Fig. 5. 15 Another way of accommodating multiple tags comprises assigning different frequencies to different tags. This way, the base can send different messages requesting responses from individual tags, one at a time. This is illustrated in Figure 8. The advantage of using this latter method is that periodical waiting is omitted. This 20 waiting can cause timing inaccuracies as the tags' operating frequencies may vary slightly. For all modes of operation in the preferred embodiments described above the tag begins to transmit as soon as possible after the condition prompting it to transmit has 25 been met. This contrasts with the operation of known tags as these typically waits a random time before sending to avoid cross-talk. In accordance with the preferred embodiments of the present invention, a random wait is unnecessary as the tags have separate, permitted transmission slots or different request signals. 30 A particularly easy and cost-effective way to provide an ultrasound transducer for the base station is to use an ordinary tag attached to the base which can be configured to communicate with the base (e.g. over a wired connection). The base can prompt the WO 2008/129295 PCT/GB2008/001412 11 transmission of an ultrasound message request simply by sending an appropriate signal to the tag's micro-controller. This way, the base knows at what time a ultrasound message request has been sent. When a response arrives, the tome-of-flight is given directly by the time difference between the request and reply. The base 5 preferably uses flank detection in order to obtain an accurate time measurement of the arrival of the tag response. Another method comprises letting the base listen for a tag request. This way, no physical connection between the base and its tag is necessary. This can be done by letting the base tag send a standard ultrasound message (with a known ID) prior to a 10 request. Taking the time between the arrival of the base tag message and the received response gives the TOF if the distance between the base detector and its transmitter tag is known. This latter method is possibly subject to more inaccuracy since two ultrasound message detections must be done. 15 A similar approach with greater accuracy is obtained by connecting the transducer of the base tag directly to one of the base channels. An exemplary protocol for the communications between the base and the tags is a 12 bit protocol with 7-bit ID, 2-bit status (movement and battery), and 3 bit cyclic 20 redundancy check (CRC) is suggested for use in the acoustic transponder system. The detector preferably uses flank detection in order to get an accurate time-stamp of the arrived tag response. Flank detection requires that the first bit is set to 0, thus restricting the ID-range to 1-31. 25 A 12 bit protocol is not essential. For example in other implementations a 28 bit protocol is used. This is also purely exemplary. Any other protocol could be used instead as appropriate. As previously mentioned the tags may be provided with a 'time-out' mode when no 30 base request is detected within a given time. The tag can then send a message even though no request is detected. For example the tag might use a different identification value when sending such a message.
WO 2008/129295 PCT/GB2008/001412 12 Experiments In an experimental arrangement comprising tags constructed in accordance with the 5 invention, the tag receiver circuit sensitivity was tested sending ultrasound at different frequencies. Preliminary tests were performed by reading out the detected frequency directly from the microcontroller. An LED was also used to indicate the frequency range of the detected signal, dividing the range into three intervals, each interval corresponding to one of three possible colors. It was observed that the listening 10 circuitry was capable of distinguishing ultrasound frequency up to at least 12 meters. Tags were programmed with the 'Wait for Request' routine set out in Fig. 3. This routine counts the number of valid frequency leaps (within restricted frequencies), and is run as long as the number of valid frequency leaps detected are below a certain 15 threshold. This way, a request signal can be generated by the base-tag by sending a number of frequencies until the tag has recorded enough leaps to reply. In a multiple tag system, each tag can listen for leaps within a certain frequency band. This way different request signals can be generated. The tests used four different frequency pairs with two different lengths. This way, eight different requests can be generated. 20 A second method consists of letting the tag listen for a certain frequency and record the length of the signal on this frequency. Using eight frequencies, each tag can listen for a unique frequency in an eight tag system. This method was found in the tests to be more sensitive than the frequency leap detection method, but suffered from echo 25 effects. During tests it was found that tags were fully capable of distinguishing ultrasound frequencies from each other using either technique. A combination of the two methods can also be used. 30 A test was also performed to check the timing, and to determine the inherent delay in transmission at the tag caused by the listening routine. This was done using the Texas WO 2008/129295 PCT/GB2008/001412 13 Instruments DaqPad tool with LabView. Signals were captured by triggering on the base-tag current and measuring the sound pressure using a microphone placed next to the responding tag. In Figure 9, the base tag current 102 vs. sound pressure 104 from the responding tag is shown. 5 The test was performed for different distances (0.5m - 6m) the responding tag pointing directly towards the requesting tag, in order to determine the constant offset. As shown in Figure 10, this offset is calculated using linear regression. Using this value (to =18.2 ms) in Equation 3 the distance can be estimated. 10 The above test shows that it is possible to estimate the distance using TOF measurements.
Claims (19)
1. An ultrasound position determination system comprising a base unit and at least one mobile unit, each of said mobile and base units operable to transmit and receive ultrasonic signals, said mobile unit being adapted to transmit a predetermined signal 5 in dependence upon the state of transmission of the base unit, said base unit being adapted to determine the time taken for said signal to pass from the mobile unit to the base unit and thereby calculate a distance between the mobile unit and the base unit.
2. An ultrasound position determination system comprising a base unit and at least 10 one mobile unit, said mobile unit being adapted to transmit an ultrasonic signal in response to a signal from the base unit, said base unit being adapted to determine the time taken for said ultrasonic signal to pass from the mobile unit to the base unit and thereby calculate a distance between the mobile unit and the base unit.
3. An ultrasound position determination system as claimed in either of claims 1 or 15 2 wherein the time taken for said ultrasonic signal to pass from the mobile unit is calculated from the aggregate time for the signal to be transmitted from the base unit to the mobile unit, and for the response to be received from the mobile unit.
4. An ultrasound position determination system as claimed in any preceding claim wherein the mobile unit is configured to detect a break in transmission by the base 20 unit and to transmit thereafter.
5. An ultrasound position determination system as claimed in claim 4 wherein the system has a plurality of mobile units, each mobile unit being assigned a unique delay from the cessation of transmission by the base unit before transmitting its signal to the base unit. WO 2008/129295 PCT/GB2008/001412 - 15
6. An ultrasound position determination system as claimed in any preceding claim wherein the mobile unit is configured to transmit as soon as possible after the condition prompting it to transmit has been met.
7. An ultrasound position determination system as claimed in any preceding claim 5 wherein the or each mobile unit is configured to detect a specific signal from the base unit.
8. An ultrasound position determination system as claimed in claim 7 comprising multiple mobile units wherein each mobile unit is configured to respond in different timeslots to the same signal from the base unit 10
9. An ultrasound position determination system as claimed in claim 7 comprising multiple mobile units wherein each mobile unit is configured to respond to a different signal from the base unit.
10. An ultrasound position determination system as claimed in any preceding claim comprising multiple mobile units wherein the mobile units are able to distinguish 15 between transmissions from the base and transmissions from other mobile units.
11. An ultrasound position determination system comprising a base unit and at least one mobile unit, said mobile unit being adapted to transmit an ultrasonic signal in response to a signal from the base unit, said base unit being adapted to determine the time taken for said ultrasonic signal to pass from the mobile unit to the base unit and 20 thereby determine whether the mobile unit is within a predetermined distance from the base unit.
12. An ultrasound position determination system as claimed in any preceding claim comprising a plurality of mobile units moveable independently of each other.
13. An ultrasound position determination system as claimed in any preceding claim 25 wherein the or each mobile unit has only one ultrasound transmitter. WO 2008/129295 PCT/GB2008/001412 - 16
14. A base unit configured to transmit a signal to a mobile unit comprising a transmitter configured to transmit a signal to one or more mobile units, and an ultrasound receiver configured to receive an ultrasonic signal from the or one of the mobile units, said base unit being adapted to determine the time taken for said 5 ultrasonic signal to pass from said mobile unit to the base unit.
15. A base unit as claimed in claim 14 configured to receive and process ultrasonic signals from only one mobile unit at a time.
16. A mobile unit comprising a receiver configured to receive a request signal from a base unit and an ultrasonic transmitter configured to transmit an ultrasonic signal 10 to said base unit after a predetermined time from receipt of said request signal.
17. A mobile unit as claimed in claim 16 wherein the mobile unit is a self-contained device containing an ultrasound transmitter and receiver and associated processing means.
18. A mobile unit as claimed in claim 16 or 17 wherein the unit further comprises 15 its own power supply.
19. A system, base station or mobile unit as claimed in any preceding claims wherein said ultrasonic signal has a frequency between 30 and 50 kHz.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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US91334707P | 2007-04-23 | 2007-04-23 | |
US60/913,347 | 2007-04-23 | ||
GB0714577.4 | 2007-07-26 | ||
GBGB0714577.4A GB0714577D0 (en) | 2007-07-26 | 2007-07-26 | Mobile object communication and position determination |
PCT/GB2008/001412 WO2008129295A1 (en) | 2007-04-23 | 2008-04-22 | Mobile object position determination |
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AU2008240366A1 true AU2008240366A1 (en) | 2008-10-30 |
AU2008240366B2 AU2008240366B2 (en) | 2012-02-23 |
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AU2008240366A Ceased AU2008240366B2 (en) | 2007-04-23 | 2008-04-22 | Mobile object position determination |
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EP (1) | EP2150835B1 (en) |
JP (1) | JP5685437B2 (en) |
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CN (1) | CN101730852B (en) |
AU (1) | AU2008240366B2 (en) |
CA (1) | CA2684986C (en) |
GB (1) | GB0714577D0 (en) |
WO (1) | WO2008129295A1 (en) |
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CA2684986C (en) | 2016-01-19 |
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CN101730852B (en) | 2013-09-04 |
JP2010525354A (en) | 2010-07-22 |
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